The serial data bus has seen widespread and ever increasing acceptance and use in the PC industry as compared to the parallel data bus. In early computers, although there was provided both a serial data interface and a parallel data interface, the parallel data interface was preferred over the serial data interface due primarily to the speed difference, this due to the fact that the data is transferred in a parallel manner. However, this parallel interface required more wires, a bulkier connector and cable, etc., whereas the serial data interfaces required smaller connectors and smaller cables. However, of course, the serial data interface transfers only a single bit of data at a time. Therefore, it is inherently slower.
To increase the speed of serial data transfer, various serial data protocols were examined. One of these was the “fire-wire” configuration, and one was the Universal Serial Bus (USB) configuration. Although fire-wire was considered to be far superior to USB, the USB interface became more popular. One of the reasons for this is the fact that it actually provides power to the peripheral device. Initially, this was not an advantage but, with later advances in such things as flash memory and low power peripheral devices, the delivery of power to a peripheral device through a Serial Data Interface became more practical. The USB interface provided this capability with up to 500 milliamps of current being made available, this providing both power in association with a serial data interface, which opened up a number of avenues for many peripheral devices. All that was required to interface with most peripheral devices on the computer was to have a USB interface. However, in order to interface the USB port on various peripheral devices with a mother board, for example, there is required some type of processing to convert the data between the serial data interface protocol and the data bus format on the mother board. The data transfer is typically what is referred to as “asynchronous” such that some type of clock synchronization is required to extract the data from a received data stream and determine a relationship between the timing of the received serial data and the timing of the mother board data, in a PC example.
In order to more easily facilitate the use of the USB with conventional devices, there have been developed certain improvements. One of these is to provide a modularized USB interface in the form of a PMCIA card. This card provides, in one example, two USB connectors of the male type on a card with a processor that allows the module to be plugged into the PMCIA slot in a computer. The PMCIA card contains thereon the necessary USB processing capability, which is powered by the computer once the PMCIA card is plugged into the PMCIA slot, this also providing power to the USB connectors.
There also provided USB modules that have disposed on board flash memory that is powered by the USB connector from the PC. These modules contain both the processing power to interface with the USB connector and the flash memory. There are also similar modules that have removable memory cards in place of the flash memories.